From BiF3 to BiF3·H2O: diverse Bi(iii) coordination for structural transformation and birefringence regulation†
Lone pair activity is an important factor to regulate the crystal structure symmetry and related optical response. Herein, a new type of hydrated bismuth fluoride, BiF3·H2O, was synthesized and characterized by a facile hydrothermal reaction. Obviously, the introduction of a water molecule significantly changed the coordination environment of Bi3+, thereby seriously changing the crystal structure of the compound BiF3. Compared with asymmetric BiFm fundamental building blocks in other compounds, BiF3·H2O possesses unprecedented near-isotropic BiF9 polyhedra and exhibits regulated birefringence values. Therefore, this work will contribute to the structural diversity of BimFn-based compounds and explore the development of new birefringent crystals.